1. Field of the Invention
The present invention relates to an imaging apparatus that is capable of capturing a synthesized image of a visible-spectrum image and an infrared-spectrum image resulting from an infrared-fluorescing substance.
2. Description of the Related Art
Fluorescent materials are used in technology for detecting the presence of specific materials or structures that are indefinite in visible-spectrum images of an object. Indocyanine green (“ICG” hereinbelow) is an example of a fluorescent material. ICG is a dye that absorbs and is excited by near-infrared light of approximately 800 nm, and fluoresces near-infrared light of approximately 850 nm. This dye can be administered to the human body as a contrast medium, and the infrared-spectrum image that is thereby observed is used during surgery, disease diagnosis, and other applications. The endoscope apparatus in, e.g., Japanese Laid-open Patent Application No. 2005-261974, can capture visible-spectrum images of the interior of body cavities and can also emit excitation light onto the subject and capture fluorescent images of the interior of body cavities of a person to whom ICG has been administered.
Japanese Laid-open Patent Application No. 2005-184690 discloses a color imaging device in which visible-spectrum pixels that are sensitive to the visible-spectrum components of red (R), green (G), and blue (B), and infrared-spectrum pixels that are essentially only sensitive to infrared-spectrum components are combined into a two-dimensional array. According to this solid-state imaging device, the signal of the infrared-spectrum pixels is used to remove offsets due to infrared-spectrum components from the signal of the visible-spectrum pixels, and a visible-spectrum image having improved color reproducibility is obtained. This solid-state imaging device can also simultaneously capture visible-spectrum images and infrared-spectrum images.
Images synthesized from normal images, which are obtained as visible-spectrum images, and infrared-spectrum images, which are based on fluorescent light, are useful for diagnosis, surgery, and other applications. The intensity of fluorescent light is usually fainter than visible light. Conventional imaging apparatuses therefore amplify the signal of the infrared-spectrum image in the solid-state imaging device and the signal-processing circuit and use a filter to attenuate the visible light incident on the solid-state imaging device, whereby the intensity balance of the visible-spectrum image and the infrared-spectrum image that are synthesized are adjusted.
However, problems have been presented in that noise increases and image quality readily deteriorates when amplifying the signal of the infrared-spectrum image in the solid-state imaging device and the signal-processing circuit, and using a filter to attenuate the visible light incident on the solid-state imaging device in order to implement a proper synthesis balance. Problems are therefore presented in that obtaining proper synthesized images from visible-spectrum images and infrared-spectrum images is difficult.